Aminothiazole derivatives useful in the preparation of β-lactam antibiotics

ABSTRACT

Aminothiazole derivatives having the carboxyl activated by means of thioesters, said derivatives being condensable with β-lactam nuclei to yield β-lactam antibiotics

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the national stage of application no.PCT/EP97/06654, filed on Nov. 28, 1997, which application claimspriority from IT MI97A002439 filed Oct. 30, 1997.

The present invention regards aminothiazole derivatives, and more inparticular aminothiazole derivatives with the carboxyl activated bymeans of thicesters, which may be used for the preparation of β-lactamantibiotics.

β-lactam antibiotics are well known in the literature, and many of them,the cephalosporins, are widely used in medical treatment, whilst manyothers are still being developed, as described in the literature, forinstance in patents WO 97/13772 and No 97/12890.

Also a large number of methods are known for the preparation ofaminothiazole cephalosporins (third generation), one of which isdescribed in the aforementioned patent WO 97/13772, where the β-lactamnucleus is condensed with a derivative of the compound having thefollowing formula:

where R is a trityl group and X is a chlorine atom, the definition“derivative” meaning that the compound (II) has the carboxyl activatedby means of chloride. The drawback of this condensation system is thatit requires a subsequent chromatographic purification phase of thecephalosporin obtained, with a consequent decrease in the yield andincrease in production costs.

In addition, in the literature activation processes are described whichemploy dicyclohexylcarbodiimide (DCC) or DCC/hydroxvbenzotriazole, butthese activation processes, besides being very costly, are not suitablefor the production of β-lactam antibiotics on an industrial scale.

Patents EP-A-037380 and EP-A-210815 describe other methods of activationon aminothiazole derivatives that are similar to those described byformula (II), but the conversion yields that may be obtained in thecondensation with the β-lactam nucleus are low.

Patent U.S. Pat. No. 4,767,852 describes aminothiazole derivatives ofcompounds of formula (II) in which the activation of the carboxyl groupis obtained by means of thioesters; in this formula, however, themeaning of X is in every case exclusively H (hydrogen): when thesederivatives are condensed, according to a method described in the patentitself, with a β-lactam nucleus, in all cases cephalosporins or β-lactamantibiotics are obtained in which X is always and exclusively H.Following the teachings of patent U.S. Pat. No. 4,767,852, it istherefore not possible to obtain all β-lactam antibiotics, such as thosedescribed in patent WO 97/13772, which are useful against the strainsproducing β-lactamase (resistant strains) in a similar way as with allother third-generation β-lactam antibiotics having an aminothiazolestructure.

The main purpose of the present invention is hence that of producingaminothiazole derivatives that may be condensed with β-lactam nuclei toyield a wide range of β-lactam antibiotics (among which those describedin patent WO 97/13772) with high levels of purity and yield.

More in particular, the invention regards aminothiazole derivativeshaving the formula

where

X is a halogen, C₁-C₄ alkyl;

Het is a 5- or 6-term heterocyclic ring having in the ring at least onehetero-atom chosen from the group made up of N, S, 0, either just as itis or condensed with a benzene ring;

R is H, C₁-C₄ aikyl, —CH₂—COOH or C(CH₃)₂—COOH, the acid functions ofwhich are free, salified or esterified, CH_(o)—CN, CH₂CF₃, CH₂F,

or a protective group of the easily removable type.

Preferably, X is Cl; Het is chosen from among the group consisting of

R is chosen from among the group consisting of trityl (Tr),tetrahydropyranyl (THP), tert-butyldimethylsilyl (TBDMS), trimethylsilyl(TMS), and methoxymethyl (MOM).

The derivatives of formula (I) may in turn be easily obtained startingfrom the corresponding acids (described in patent WO 97/13772) accordingto the procedure described in patent U.S. Pat. No. 4767852.

The aminothiazole derivatives (I) may be easily condensed with β-lactamnuclei (is necessary, protected) to give β-lactam antibiotics withcomplete retention of the stereochemistry of the oxime formula C═N—OR(and hence with high levels of purity and high yields).

In particular, it may be noted that the condensation reaction of thederivatives (I) with the β-lactam nuclei may be conducted attemperatures of between −30° C. and +80° C., preferably of between −5°C. and +40° C., using highly polar organic solvents (pure, or mixedtogether, or mixed with water up to 50% of water, also in two-phasesystems) capable of solubilizing (even only partially) the reagents (inparticular the derivatives I), such as methylene chloride, ethylacetate, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone,acetone, dimethyl sulphoxide, methanol, ethanol, isopropanol, andsulpholane, having a high dielectric constant. The examples that followare illustrative of the present invention.

EXAMPLE 1 Preparation of (Z)-2-aminothiazolyl-5-chloro-α-trityloximinoacetate of 2-mercaptobenzothiazolyl

To 900 mlit of methylene chloride are added at room temperature 245 g ofbenzothiazole disulphide and 193 g of triphenylphosphine and, under faststirring, 355 g of (Z)-2-aminothiazolyl-5-chloro-α-trityloximino aceticacid (273 g of activity)—which is a compound of formula (II) where X isCl and R is trityl—obtained according to what is described in WO97/13772. The reaction is exothermic, the temperature risingspontaneously to 35° C. After 10 minutes, the above is left under slowstirring, and the product, as it forms, crystallizes. The reaction iscomplete in the course of 1 hour (35° C.). At the end of the reaction,cool off to 15° C. and leave under stirring for 1 hour. Filter and washwith 600 mlit of methylene chloride. Dry in a vacuum at 40° C., untilconstant weight is reached.

In this way, 322 g of the product of formula (I) are obtained in which Xis Cl, R is trityl and Het is benzothiazolyl.

Melting point, 170° (decomposition) ¹H NMR (solvent DMSO D6 ISTDtetramethylsilane) 8.26/8.23 ppm (1H, m); 8.11/8.08 ppm (1H, m);7.64/7.27 ppm (19H, m).

EXAMPLE 2 Preparation of (Z)-2-aminothiazolyl-5-chloro-α-trityloximinoacetate of 2-mercaptobenzothiazolyl

The reaction is conducted as in the previous example, except for thefact that 75 g of triethylamine are added in the course of the reaction.In this way, 315 g of product are obtained having the samechemico-physical characteristics.

EXAMPLE 3 Preparation of7-β-[(Z)-2-aminothiazolyl-5-chloro-α-trityloximinoacetamide]-3-chloro-cephalosporanic acid sodium salt

Suspend 6 g of 3-Cl-7-amino-cephalosporanic acid in 50 mlit of methylenechloride and protect as trimethylsilyl ester according to proceduresdescribed in the literature (Pierce, “Silylation of Organic Compounds”,Pierce Chem. Co. Rockford III; J. Am. Chem. Soc. 85, 2497, 1963). Dilutethe silylated product with 50 mlit of dimethyl acetamide, add 15 g ofthioester obtained as described in the foregoing, example, and leave toreact at room temperature overnight. Correct the pH to 6.5 with soda andwash the organic phase with a 10% sodium chloride aqueous solution (80mlit for five times).

Evaporate the organic phase until an oil is obtained, which is dilutedwith 100 mlit of isopropanol so as to crystallize the product. Filterand wash with isopropanol.

After drying, 30.5 g are obtained of product having an HPLC purity of96.7%.

Melting point, 165° (decomposition) ¹H NMR (solvent DMSO D₅ ISTDtetramethylsilane) 9.92/9.89 (1H, d); 7.34/7.19 (17H, m); 6.04/6.00 (1H,dd); 5.32/5.30 (1H, d); 4.02/3.66 (2H, AB)

EXAMPLE 4 Preparation of7-β-[(Z)-2-aminothiazolyl-5-chloro-α-trityloximinoacetamide]-3-chloro-cephalosporanic acid para-nitrobenzyl ester

Dissolve 12 g of thioester obtained according to Example 1 or Example 2in 130 mlit of dimethylformamide. Add 6.6 g of 7-amino-3-chlorocephalosporanic acid para-nitrobenzyl ester.

Leave to react overnight at room temperature; dilute with 150 miit ofethyl acetate and wash repeatedly with water to extract all the DMF.Decolour the solution with 1 g of carbon, filter, and wash with acetate.Evaporate the rich phase in a vacuum until an oil is obtained, anddilute with 200 mlit of absolute ethanol.

Heat up to complete dissolution and then leave to cool down untilprecipitation of the product. Filter and wash with methanol and dryuntil constant weight is achieved. In this way, 10.1 g of product areobtained having an HPLC purity of 97.8%.

Melting point, 177° C. (decomposition) ¹H NMR (DMSO D6ISTD=tetramethylsilane) 9.93/9.90 (1H, d); 8.28/8.25 (2H, d); 7.74/7.71(2H, d); 7.35/7.25 (17H, m); 6.11/6.07 (1H, dd); 5.49 (2H, s); 5.37/5.35(1H, d); 4.08/3.75 (2H, AB).

EXAMPLE 5 Preparation of 7-β-[(Z)-2-aminothiazolyl-5-chloro-α-trityloximino acetamide]-3-methoxymethylcephalosporanic acid sodium salt

Suspend 100 g of 3-methoxymethyl-7-amino-cephalosporanic acid in amixture consisting of 2.1 lit of DMF and 300 muit of water. Add 270 g ofthioester obtained according to Example 1 or Example 2, and then allow68 mlit of TEA to drip over a period of 1 hour. Leave to react overnightat room temperature. At the end of the reaction, dilute with 2 lit ofethyl acetate and 1.5 lit of salt-saturated water. Bring the pH down to3 with hydrochloric acid, separate the phases and wash the organic phasemore than 3 times with 1 lit of salt water each time.

Evaporate the organic phase in a vacuum until the residue is obtained.Dilute with 1 lit of ethyl acetate and add 68 g of sodium 2-ethylhexanoate; the sodium salt of the product precipitates immediately.Filter and wash with ethyl acetate.

After drving, 265 g of product are obtained having an HPLC purity of98.5%.

Melting point, 180° (decomposition) ¹H NMR (DMSO D6 18 TDtetranethylsilane) 9.92/9.90 (1H, d); 7.31/7.23 (17H, m); 5.95/5.91 (1H,dd); 5.24/5.23 (1H, d); 4.2 (2M, s); 3.64/3.46 (2H, AB); 3.2 (3H, s).

What is claimed is:
 1. An aminothiazole compound of formula

where: X is a halogen; Het is a 5- or 6-membered heterocyclic ringhaving in the ring at least one hetero-atom chosen from the group madeup of N, S and O, either just as it is or condensed with a benzene ring;R is H, C₁-C₄ alkyl, —CH₂—COOH or C(CH₃)₂—COOH, the acid functions ofwhich are free, salified or esterified, CH₂—CN, CH₂CF₃, CH₂F,

 or a protective group of the easily removable type which is chosen fromamong the group consisting of trityl (Tr), tetrahydropyranyl (THP),tert-butyldimethylsilyl (TBDMS), trimetylsilyl (TMS), and methoxymethyl(MOM).
 2. A compound according to claim 1, where X is Cl.
 3. A compoundaccording to claim 1, where Het is chosen from among the groupconsisting of


4. A compound according to claim 2, where R is chosen from among thegroup consisting of trityl (Tr), tetrahydropyranyl (THP),tert-butyldimethylsilyl (TBDMS), trimethylsilyl (TMS), and methoxymethyl(MOM).
 5. A compound according to claim 2 where Het is chosen from amongthe group consisting of